Traditionally, most commercially available inkjet printers have a print engine which forms part of the overall structure and design of the printer. The body of the printer unit is typically constructed to accommodate the printhead and associated media delivery mechanisms, and these features are integral with the printer unit.
This is especially the case with inkjet printers that employ a printhead that traverses back and forth across the media as the media progresses through the printer unit in small iterations. Typically, the reciprocating printhead is mounted to the body of the printer unit such that it can traverse the width of the printer unit between a media input roller and a media output roller, with the media input and output rollers forming part of the structure of the printer unit. It may be possible to remove the printhead for replacement, however the other parts of the print engine, such as the media transport rollers, control circuitry and maintenance stations, are usually fixed within the printer. Replacement of these parts is not possible without replacement of the entire printer.
As well as being rather fixed in their design construction, printers employing reciprocating type printheads are relatively slow, particularly when performing print jobs of full colour and/or photo quality. This is due to the fact that the printhead must continually scan the stationary media to deposit the ink on the surface of the media and it may take a number of swathes of the printhead to deposit one line of the image.
Recently, ‘pagewidth’ printheads have been developed that extend the entire width of the print media. The printhead remains stationary as the media is transported past its array of nozzles. This increases print speeds as the printhead no longer needs to perform a number of swathes to deposit a line of an image. Instead, the printhead deposits the ink on the media as it moves past at high speeds. With these printheads, full colour 1600 dpi printing at speeds of around 60 pages per minute are possible. Such speeds were unattainable with conventional inkjet printers.
Printing at these speeds generates a significant amount of heat. As the various components within the printer heat up from an ambient temperature to an operating temperature, they expand in accordance with the coefficient of thermal expansion (CTE) of the material with which they are made. This is particularly problematic for pagewidth printheads because of their elongate configuration. The total expansion of the printhead in the longitudinal direction can be relatively high. As there are many different components making up a printhead assembly, each component with its own CTE, any mismatches in expansion can induce bending stresses in the overall structure that are ultimately detrimental to print quality. To avoid this, every component in the printhead assembly can be fabricated from materials with the same or very similar CTE's. However, as the nozzles are MEMS structures fabricated on a silicon wafer using lithographic etching and deposition techniques, the materials CTE's close to that of silicon are relatively expensive and difficult to fabricate and assemble.